In typical prior building management systems the transmission of control and sensor information has been handled in several ways. As an example, one system is provided with an unduly large number of transmission wires interconnecting the major components in the subsystem with inefficient addressing, relatively slow relay operation, the greater numbers of wires normally tending to make the system more expensive than other systems. In order to avoid the multiplicity of wires situation, other systems have incorporated as few as a pair of wires for handling all information but this requires a serial transmission of control and sensor information with longer time required for such transmission. Encoding and decoding circuits for a system of this nature are more complicated. Thus, inefficiencies are encountered in systems of this nature, as well.
Of further interest, prior systems have provided automated operation but not necessarily a desirable level of manual intervention in the system.
Considering the Input/Output aspects of prior subsystems, ordinarily various significant components have been incorporated in the cabinets in such a manner that they are separately mounted, requiring additional cabling for proper interconnection. In many cases, less flexibility in functions and limited maintenance are encountered.